1. Field of the Invention
This invention relates to a covering for a machine for treating a material web, in particular a fibrous web. Also, it relates to special uses of this covering.
2. Description of the Related Art
To date, coatings of transfer belts for use in paper machines are produced mainly by way of knife coating methods. In this case polymers are applied and knife-coated two-dimensionally onto a textile carrier which in most cases is based on a press felt. A film solution in which polyurethane films are endlessly welded in the transverse direction and then wound around a carrier has already been proposed. The carrier in question is a conventional felt-based fabric which is combined with fleece layers and a so-called “Arcus” thread layer. However, this proposal has turned out to be inclined toward delamination, as the carrier layer onto which the films are laminated becomes detached in conditions of high shear stress such as can arise in particular in a press nip. Delamination then occurs as the result. One of the reasons for this is that the applied polyurethane films are unable, because of their small thickness, to create a genuine form-fit connection with the threads or fleeces lying underneath or to enter into a bond with each other. Furthermore, the process provided to date is relatively difficult to reproduce on account of its complexity, as the result of which the process results vary from one manufactured belt to the next.
What is needed is an improved covering of the type initially referred to. The covering can be manufactured in an easier manner. Furthermore, the functionality of the covering can be enhanced in the case of a transfer belt for example, in particular for critical applications such as a double nip for example, in a so-called center belt application for example.